Pattern match sewing machine

Abstract

A device for sewing together two fabric parts includes two pattern sensors and correcting means for determining and correcting misalignment of patterns on the fabric parts. Also, an additional image sensor (18) is provided, which scans the surface of the fabric (16) to be sewn at the site of an intermediate storage location (15) before this fabric is fed into the sewing machine. An image-processing device connected to this additional image sensor generates data on certain basic characteristics of the fabric pattern, such as color, contrast, lightness, register length, and angular orientation of the pattern components. From these characteristic data, a decision logic circuit determines setting data for the operating parameters of the devices used in the sewing machine for detecting and correcting a possible pattern misalignment during sewing.

What is claimed is: 
     
       1. A device for sewing together two fabric parts according to a pattern on the fabric parts, comprising: a sewing machine including a separate feed mechanism for feeding each of the two fabric parts to be sewn together; two separate pattern sensors located adjacent a stitch formation site of the sewing machine, each of said two separate pattern sensors optically scanning a fabric part in at least one predetermined direction relative to an edge of the fabric part to be sewn and generating a pattern signal representing pattern-dependent variations in light intensity; correcting means for determining a one-dimensional or two-dimensional misalignment of the patterns of the two fabric parts by comparative analysis of a pattern signal of each of the two pattern sensors and acting on at least one of said feed mechanisms to correct said misalignment; setting means for setting operation parameters of a functional group formed by the pattern sensors and said correcting means as a function of basic characteristics of the patterns of the fabric parts; an additional image sensor positioned for viewing a site at which fabric parts are temporarily stored before being fed to said sewing machine, said additional image sensor optically scanning a pattern of a fabric part located at said site and generating a corresponding image signal; an image signal processing device for generating characteristic data from said image signal, said characteristic data corresponding to basic characteristics of the pattern scanned; a memory device receiving said characteristic data from said image processing device and storing said characteristic data; a decision logic circuit for generating setting data for said operating parameters based on said characteristic data, said operating parameters being sent to said setting means; and, transfer means, activated before a beginning of a sewing process for sending said characteristic data from said memory device to said decision logic circuit. 
     
     
       2. A device according to claim 1, wherein said setting means includes a final control element for amplifying an amplitude offset of said two pattern signals; said image processing device generating data including lightness contrast and average lightness of a pattern scanned based on said image signal of the additional image sensor; said decision logic circuit generating setting data for said final control element for controlling amplification and offset based on said lightness contrast and average lightness data. 
     
     
       3. A device according to claim 1, wherein said setting means includes a color selection device for selectable analysis of light of different colors in each of said two separate pattern sensors; said additionally provided image sensor being provided as a light-discriminating sensor; said image processing device supplying data in the form of color data based on the colors of the components of a pattern scanned; said decision logic circuit generating setting data based on said color data for selecting a color in which pattern-dependent amplitude differences of pattern signals have their maximum. 
     
     
       4. A device according to claim 3, wherein said color selection device includes a plurality of narrow-band color filters insertable into a path of rays of each of said two separate pattern sensors. 
     
     
       5. A device according to claim 1, wherein said correcting device is switchable between one of two different algorithms for determining pattern misalignment; said logic circuit generating said setting data for selecting a most suitable algorithm in a particular case based on characteristic data generated by said image processing device. 
     
     
       6. A device according to claim 5, wherein said characteristic data generated by said image-processing device includes data representing edge sharpness of components of the pattern scanned. 
     
     
       7. A device according to claim 1, wherein said setting means includes inputs for entering at least one computation parameter, said correcting device including at least one algorithm using said computation parameter as an independent variable characteristic of an actual pattern of the fabric part scanned by said additionally provided image sensor; said image processing device generating data for determining said computation parameter; said decision logic circuit determining said computation parameter based on said characteristic data. 
     
     
       8. A device according to claim 7, wherein one element of said characteristic data obtained to determine said computation parameter is an angular orientation of stripes of a pattern relative to an edge to be sewn. 
     
     
       9. A device according to claim 8, wherein said algorithm used by said correcting means to compute pattern misalignment includes the formation of a cross-correlation function of pattern signals of the two pattern sensors, said setting means setting a threshold for said correlation function depending on a computation parameter representing said angular orientation. 
     
     
       10. A device according to claim 7, wherein one element of said characteristic data used for determining said computation parameter is a register length of a pattern scanned by said additionally provided image sensor. 
     
     
       11. A device according to claim 10, wherein said algorithm used in said correcting device to compute pattern misalignment includes the formation of a cross-correlation function of pattern signals of said two pattern sensors, said setting means setting a pattern block length for computing said cross-correlation function depending on said computation parameter representing the register length. 
     
     
       12. A device according to claim wherein said image processing device drives data corresponding to a spatial frequency of an optically recognizable period structure of the pattern scanned in a given pattern direction, said period structure being denser than a pattern structure to be detected for misalignment correction; said decision logic circuit including an input for said spatial frequency data and for information on a current feed velocity of the fabric parts in the sewing machine in order to determine a product of the spatial frequency and an actual feed velocity; a controllable low-pass filter including a control input receiving a control signal corresponding to said product from the decision logic circuit, for adjusting a limit frequency of the low-pass filter, said low-pass filter suppressing a frequency corresponding to said product, said low-pass filter filtering said pattern signal from said two pattern sensors as said pattern signal is sent to said correcting device. 
     
     
       13. A device according to claim 1, wherein said additionally provided image sensor includes a two-dimensional sensor with an optical system arranged in front of it, said optical system images an area of an inserted fabric part onto the light-receiving surface of the image sensor, said area being at least slightly larger than a register length of the pattern in a predetermined scanning direction. 
     
     
       14. A device according to claim 1, wherein said additionally provided image sensor scans in two predetermined scanning directions in the plane of the fabric parts, one scanning direction being parallel to an edge to be sewn and another scanning direction being perpendicular to an edge to be sewn.